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Recent advances in high-speed intracoronary optical coherence tomography (OCT) have enabled visualization of 3-dimensional (3D) microstructure of long coronary artery segments in vivo (1); however, imaging speed remains insufficient to avoid detrimental cardiac motion artifacts in imaging that spans several cardiac cycles during a pullback, limiting the clinical utility of OCT (2). In addition, the large amount of radiocontrast media used for blood flushing conveys a risk of acute kidney injury. In this study, we report the early experience of high-speed OCT for cardiac motion-free intracoronary imaging in a beating swine heart.

The laboratory-built, high-speed intracoronary OCT comprises an imaging system with an A-line rate of 243 kHz (3), a fiber-optic rotary coupler that sustains rotational speeds up to ∼500 revolution/s, and an imaging catheter with a rigid distal length of 3 mm and an outer diameter of 0.87 mm. To avoid bulk cardiac motion during imaging, we implemented prospective triggering using the electrocardiography (ECG) signal. For the starting point of data acquisition and pullback, we gave a relative phase delay (60% of R-R interval) after the final R-wave, which enabled skipping of the QRS complex and T-wave. Accordingly, images recorded during 30% to 40% of the cardiac cycle (a single late diastolic phase) were presumed to be cardiac motion free. For intracoronary imaging in vivo, a male Yorkshire pig (weight 30 kg) was anesthetized and mechanically ventilated. A drug-eluting stent (2.5 × 14 mm) was implanted within the left anterior descending artery. ECG-triggered high-speed imaging (500 frames/s, 100 mm/s) was performed repeatedly (n = 5). To mimic conventional OCT operation, low-speed imaging (100 frames/s, 20 mm/s) was also performed (n = 3). For clearance of intracoronary blood, iodinated contrast was automatically injected at 3 ml/s during imaging.

In the longitudinal section of ECG-triggered high-speed imaging, the coronary vessel contour appeared smooth and free of discontinuities through the entire pullback length (Figure 1A). However, in conventional-speed imaging (Figure 1B), the vascular contour was severely distorted at locations that corresponded to systolic and diastolic motion. The cross-sectional OCT images obtained using the high-speed protocol showed comparable resolution, contrast, and depth of penetration compared with conventional-speed imaging. Cutaway longitudinal and fly-through views of the 3D volume rendering revealed the advantage of high-speed OCT more clearly. The 3D architecture of the coronary artery, stent, and guidewire were smoother and more realistic in the ECG-triggered high-speed imaging (Figure 1C), whereas the 3D vessel contour appeared inaccurate in conventional imaging (Figure 1D). The stent and guidewire looked severely distorted by cardiac motion. Furthermore, the amount of contrast dye delivered by automatic injector during pullback was much smaller in high-speed imaging than in conventional imaging (14 ± 1 ml vs. 21 ± 2 ml, p = 0.01).

The combination of the high-speed OCT system, high-speed rotary coupler, optimized high-speed imaging catheter, and prospective ECG triggering has facilitated coronary artery imaging at a rate of 500 frames/s and a pullback speed of 100 mm/s, enabling imaging of a long coronary artery segment during the period of minimal motion artifact within a single cardiac cycle (70 mm pullback in 0.7 s). In addition, the short imaging time decreased the amount of contrast dye required for blood clearing, which would reduce the risk of contrast-induced nephropathy.

Our study has several limitations. First, this was a proof-of-principle study with a limited number of experiments. Second, the system was not tested for elevated heart rates, which might have shorter motion-free time windows. Third, the image acquisition was not automatically synchronized with blood flushing. The synchronization of blood flushing and image acquisition along with ECG triggering would further decrease the volume of contrast dye required.

Footnotes

Please note: This study was supported by the National Research Foundation of Korea (grant 2010-0017465, grant 2012R1A2A2A04046108, and Global PhD Fellowship Program [2012H1A2A1010075]), the Ministry of Science, ICT and Future Planning of Korea (grant NIPA-2013-H0401-13-1007), and the National Institutes of Health (grant P41 EB015903). The first 3 authors (Dr. S.-J. Jang, H.-S. Park, and J.W. Song) contributed equally to this work. Drs. W.-Y. Oh and J.W. Kim are joint senior authors.